Influence of alkalinity and temperature on photosynthetic biogas upgrading efficiency in high rate algal ponds

Performance evaluation of a control strategy for photosynthetic biogas upgrading in a semi-industrial scale photobioreactor

“…Moreover, digestate from anaerobic digestion, a nutrient-rich effluent from the process, can be used as N and P source to support microalgal/bacterial growth, which improves the environmental and economic sustainability of this green technology (Ouyang et al, 2015). The optimization of photosynthetic biogas upgrading coupled with nutrient recovery from digestates, which is commonly implemented in a bubble biogas scrubbing column (AC) interconnected via culture broth recirculation to a photobioreactor where the absorbed CO 2 and H 2 S uptake occurs, has been carried out under indoors conditions at lab scale (Bahr et al, 2014;Franco-Morgado et al, 2017;Meier et al, 2018;Rodero et al, 2018;Serejo et al, 2015). Nevertheless, the performance of outdoors systems is governed by the daily and seasonal variations in environmental conditions, the pH in the cultivation broth being a critical parameter that impacts on both H 2 S and CO 2 gas-liquid mass transfer in the AC (Bose et al, 2019;Posadas et al, 2017).…”

Integral (VOCs, CO2, mercaptans and H2S) photosynthetic biogas upgrading using innovative biogas and digestate supply strategies

“…Furthermore, the L/G ratio in this particular HRAP-AC configuration which has been identified as the main operational parameter determining the final quality of biomethane was optimized (L/G ratio=0.5). In this context, L/G ratios lower than 1.0 minimize O 2 and N 2 stripping from the cultivation broth but entail a severe acidification of the recirculating medium (that can ultimately decrease the removal efficiencies of CO 2 and H 2 S), unless a sufficiently high alkalinity is present in the cultivation broth [23]. In addition, low L/G ratios are beneficial from an energy-reduction viewpoint and would contribute to decreasing the overall operating cost of the photosynthetic biogas upgrading.…”

Integrated innovative biorefinery for the transformation of municipal solid waste into biobased products

“…This technology has been recently optimized in a 180 L HRAP indoors and outdoors in the context of domestic wastewater treatment, with a consistent production of a biomethane complying with most international regulations (CH 4 > 95%, CO 2 < 1%, N 2 < 3%, O 2 < 0.5%), and has been up-scaled in the URBIOFIN biorefinery in a 300 m 2 HRAP interconnected to a 0.5 m 3 absorption column fed with 12 m 3 /d of biogas and 0.1 m 3 /d of liquid fraction of digestate from the AD of OFMSW. The ratio between the biogas flow rate and the liquid recirculation flow rate in the absorption column, and the pH and alkalinity of the cultivation broth in the HRAP, have been consistently shown as the most relevant operational parameters determining biomethane quality in this innovative biotechnology [52]. Overall, photosynthetic biogas upgrading in algal-bacterial photobioreactors could decrease the operating costs of conventional biogas upgrading (H 2 S adsorption by activated carbon filtration þ CO 2 removal by water absorption) from 0.2 V/Nm 3 to 0.03 V/Nm 3 , with a concomitant decrease in the energy demand from 0.3 kWh/Nm 3 to 0.08 kWh/Nm 3 [53].…”